Semiconductor device and method for producing the same

ABSTRACT

A semiconductor region having an upper surface and a side surface is formed on a substrate. A first impurity region is formed in an upper portion of the semiconductor region. A second impurity region is formed in a side portion of the semiconductor region. The resistivity of the second impurity region is substantially equal to or smaller than that of the first impurity region.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of Application PCT/JP2008/50253, filed on Jan.11, 2008.

FIELD OF THE INVENTION

The present invention relates to a semiconductor device and a method forproducing the same, and more particularly to a semiconductor device of athree-dimensional structure including fin-shaped semiconductor regionson a substrate and a method for producing the same.

BACKGROUND ART

In recent years, demands for miniaturizing semiconductor devices havebeen increasing along with the increase in the degree of integration,functionality and speed thereof. In view of this, various devicestructures have been proposed in the art, aiming at the reduction in thearea of the substrate taken up by transistors. Among others, attentionhas been drawn to field effect transistors having a fin-shapedstructure. A field effect transistors having the fin-shaped structure iscommonly called a fin-shaped FET (field effect transistor), and has anactive region including thin wall (fin)-like semiconductor regionsperpendicular to the principle plane of the substrate. In a fin-shapedFET, the side surface of the semiconductor region can be used as achannel surface, whereby it is possible to reduce the area on thesubstrate taken up by the transistor (see, for example, Patent Document1 and Non-Patent Document 1).

FIG. 16A to FIG. 16D show a structure of a conventional fin-shaped FET,wherein FIG. 16A is a plan view of the device, FIG. 16B is across-sectional view taken along line A-A in FIG. 16A, FIG. 16C is across-sectional view taken along line B-B in FIG. 16A, and FIG. 16D is across-sectional view taken along line C-C in FIG. 16A.

As shown in FIG. 16A to FIG. 16D, a conventional fin-shaped FET includesa supporting substrate 101 made of silicon, an insulating layer 102 madeof silicon oxide formed on the supporting substrate 101, semiconductorregions 103 a to 103 d each formed into a fin shape on the insulatinglayer 102 (hereinafter referred to as the “fin-shaped semiconductorregions”), a gate electrode 105 formed on the fin-shaped semiconductorregions 103 a to 103 d via gate insulating films 104 a to 104 d,insulative sidewall spacers 106 formed on side surfaces of the gateelectrode 105, extension regions 107 formed on opposite side regions ofthe fin-shaped semiconductor regions 103 a to 103 d sandwiching the gateelectrode 105 therebetween, and source-drain regions 117 formed onopposite side regions of the fin-shaped semiconductor regions 103 a to103 d sandwiching the gate electrode 105 and the insulative sidewallspacer 106 therebetween. The fin-shaped semiconductor regions 103 a to103 d are placed on the insulating layer 102 so as to be arranged atregular intervals in the gate width direction. The gate electrode 105 isformed so as to extend across the fin-shaped semiconductor regions 103 ato 103 d in the gate width direction. The extension region 107 includesa first impurity region 107 a formed in an upper portion of each of thefin-shaped semiconductor regions 103 a to 103 d, and a second impurityregion 107 b formed in a side portion of each of the fin-shapedsemiconductor regions 103 a to 103 d. The source-drain region 117includes a third impurity region 117 a formed in an upper portion ofeach of the fin-shaped semiconductor regions 103 a to 103 d, and afourth impurity region 117 b formed in a side portion of each of thefin-shaped semiconductor regions 103 a to 103 d. Note that pocketregions are not described herein or shown in the figure.

FIG. 17A to FIG. 17D are cross-sectional views, showing, step by step, aconventional method for producing a semiconductor device. Note that FIG.17A to FIG. 17D correspond to the cross-sectional structure taken alongline C-C in FIG. 16A. In FIG. 17A to FIG. 17D, like elements to thoseshown in FIG. 16A to FIG. 16D are denoted by like reference numerals andwill not be described again.

First, as shown in FIG. 17A, there is provided an SOI (silicon oninsulator) substrate, in which the insulating layer 102 made of siliconoxide is provided on the supporting substrate 101 made of silicon, and asemiconductor layer made of silicon is provided on the insulating layer102. Then, the semiconductor layer is patterned to form the fin-shapedsemiconductor region 103 b to be the active region.

Then, as shown in FIG. 17B, the gate insulating film 104 is formed onthe surface of the fin-shaped semiconductor region 103 b, after which apolysilicon film 105A is formed across the entire surface of thesupporting substrate 102.

Then, as shown in FIG. 17C, the polysilicon film 105A and the gateinsulating film 104 are etched successively to form the gate electrode105 on the fin-shaped semiconductor region 103 b with the gateinsulating film 104 b interposed therebetween. Then, using the gateelectrode 105 as a mask, the semiconductor region 103 b is ion-implantedwith an impurity to form the extension region 107 and the pocket region(not shown).

Next, as shown in FIG. 17D, an insulating film is formed across theentire surface of the supporting substrate 102, and then the insulatingfilm is etched back by using anisotropic dry etching to thereby form theinsulative sidewall spacer 106 on the side surface of the gate electrode105. Then, using the gate electrode 105 and the side wall 106 as a mask,the semiconductor region 103 b is ion-implanted with an impurity to formthe source-drain region 117.

Through the steps described above, it is possible to obtain a fin-shapedMISFET (metal insulator semiconductor field effect transistor) havingthe gate electrode 105 formed on the fin-shaped semiconductor region 103b with the gate insulating film 104 b interposed therebetween.

[Patent Document 1] Japanese Laid-Open Patent Publication No.2006-196821

[Non-Patent Document 1] D. Lenoble, et al., Enhanced performance of PMOSMUGFET via integration of conformal plasma-doped source/drainextensions, 2006 Symposium on VLSI Technology Digest of TechnicalPapers, p. 212

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, with conventional methods for producing a semiconductor devicedisclosed in documents such as Patent Document 1 and Non-Patent Document1 identified above, it is not possible to obtain desirable transistorcharacteristics In view of this, it is an object of the presentinvention to realize a semiconductor device including fin-shapedsemiconductor regions with which desirable characteristics can beobtained (e.g., a device which does not exhibit a substantial reductionin drain current).

Means for Solving the Problems

In order to achieve the object set forth above, the present inventorshave studied the reason why desirable transistor characteristics cannotbe obtained with the conventional methods for producing a fin-shapedFET, which lead to the following findings.

FIG. 18A is a cross-sectional view of an important part showing the stepof forming an extension region of a fin-shaped FET as described inPatent Document 1, and FIG. 18B is a cross-sectional view showing thestep of forming an extension region of a fin-shaped FET as described inNon-Patent Document 1. Note that FIG. 18A and FIG. 18B correspond to thecross-sectional structure (before the formation of the insulativesidewall spacer 106) taken along line B-B in FIG. 16A. In FIGS. 18A and18B, like elements to those shown in FIG. 16A to FIG. 16D are denoted bylike reference numerals.

As shown in FIG. 18A, in the method disclosed in Patent Document 1, inorder to introduce an impurity not only into the upper surface of thefin-shaped semiconductor regions 103 a to 103 d but also into the sidesurface thereof, ions 108 a and 108 b are implanted by ion implantationinto the fin-shaped semiconductor regions 103 a to 103 d at respectiveimplantation angles inclined with respect to the vertical direction indifferent directions from each other, thus forming the extension region107. In such a case, the first impurity region 107 a, into which theions 108 a and the ions 108 b are both implanted, is formed in the upperportion of the fin-shaped semiconductor regions 103 a to 103 d. However,the second impurity region 107 b, into which either the ions 108 a orthe ions 108 b are implanted, is formed in each side portion of thefin-shaped semiconductor regions 103 a to 103 d. Thus, where the dose ofthe ions 108 a and that of the ions 108 b are equal to each other, theimplantation dose of the first impurity region 107 a is twice as largeas the implantation dose of the second impurity region 107 b.

As shown in FIG. 18B, in the method disclosed in Non-Patent Document 1,the extension region 107 is formed in the fin-shaped semiconductorregions 103 a to 103 d by using a plasma doping method. Where animpurity is implanted by using a plasma doping method, the firstimpurity region 107 a is formed in an upper portion of the fin-shapedsemiconductor regions 103 a to 103 d, wherein the implantation dose ofthe first impurity region 107 a is dictated by the balance betweenimplanted ions 109 a, an adsorbed species (a neutral species such as gasmolecules or radicals) 109 b, and an impurity 109 c that is desorbedfrom the fin-shaped semiconductor regions 103 a to 103 d by sputtering.However, the implantation dose of each side portion of the fin-shapedsemiconductor regions 103 a to 103 d is less influenced by the implantedions 109 a and the impurity 109 c desorbed by sputtering, and there isformed the second impurity region 107 b whose implantation dose ismainly dictated by the adsorbed species 109 b. As a result, theimplantation dose of the first impurity region 107 a is higher than thatof the second impurity region 107 b by about 25%, for example.

As described above, with the conventional methods for forming anextension region of a fin-shaped FET, the implantation dose of the firstimpurity region 107 a formed in an upper portion of the fin-shapedsemiconductor regions 103 a to 103 d is higher than that of the secondimpurity region 107 b formed in a side portion of the fin-shapedsemiconductor regions 103 a to 103 d. Moreover, the junction depth ofthe second impurity region 107 b is shallower than that of the firstimpurity region 107 a. Accordingly, the sheet resistance, theresistivity, or the spreading resistance of the first impurity region107 a is lower than the sheet resistance, the resistivity, or thespreading resistance of the second impurity region 107 b. Wherein,Rs=ρ/t is satisfied where Rs is a sheet resistance of a target, ρ is aspecific resistance (resistivity), t is a thickness (junction depth),and ρw is a spreading resistance. Further, as expressed by therelational expression, ρw=CF·k·ρ/2πr, which is widely known in the artof spreading resistance measurement, proportion of Rs to ρw/t is lead(i.e., main component) since the specific resistance (resistivity) ρ andthe spreading resistance ρw are basically in one to one correspondence.In the relational expression, CF is a correction factor with the volumeeffect of the spreading resistance ρw taken into consideration (wherein,with no correction, CF is 1), k is a correction factor with the polaritydependency in Schottky barrier between a probe and a sample taken intoconsideration (for example, k is 1 when a sample is made of p-typesilicon, or k is any of 1 to 3 when a sample is made of n-type silicon),and r is a radius of curvature of the tip end of a probe.

When a fin-shaped FET having such an extension structure is operated,the current flowing through the extension region 107 is localized in thefirst impurity region 107 a where the implantation dose is higher, i.e.,the sheet resistance is lower, than the second impurity region 107 b,thereby failing to obtain desirable transistor characteristics.

Moreover, in the conventional fin-shaped FET, the source-drain region isalso formed by using an ion implantation method or a plasma dopingmethod similar to that for the extension region. Therefore, also in thesource-drain region 117, the implantation dose of the third impurityregion 117 a formed in an upper portion of the fin-shaped semiconductorregions 103 a to 103 d is higher than that of the fourth impurity region117 b formed in a side portion of the fin-shaped semiconductor regions103 a to 103 d. Moreover, the junction depth of the fourth impurityregion 117 b is shallower than that of the third impurity region 117 a.When a fin-shaped FET having such a source-drain structure is operated,the current flowing through the source-drain region 117 is localized inthe third impurity region 117 a where the implantation dose is higher,i.e., the sheet resistance is lower, than the fourth impurity region 117b, thereby failing to obtain desirable transistor characteristics.

Based on the above findings, the present inventors have invented asemiconductor device including an impurity region in a side portion of afin-shaped semiconductor region where the implantation dose issubstantially equal to or greater than that in an upper portion of thefin-shaped semiconductor region, and a method for producing the same.Particularly, in some cases with a fin-shaped FET, the width of theimpurity region formed in a side portion of the fin-shaped semiconductorregion accounts for 70% or more of the width of the extension region andthe source-drain region in the gate width direction. Therefore, it hasbecome important that the implantation dose of the impurity regionformed in a side portion of the fin-shaped semiconductor region is madesubstantially equal to or greater than that of the impurity regionformed in an upper portion of the fin-shaped semiconductor region. Inother words, it is important to set the resistivity, the spreadingresistance, or the sheet resistance of the impurity region formed in theside portion of the fin-shaped semiconductor region to be equal to orsmaller than the resistivity, the spreading resistance, or the sheetresistance of the impurity region formed in the upper portion of thefin-shaped semiconductor region.

Specifically, a first semiconductor device of the present invention is asemiconductor device, including: a first semiconductor region formed ona supporting substrate and having an upper surface and a side surface; afirst impurity region of a first conductivity type formed in an upperportion of the first semiconductor region; and a second impurity regionof a first conductivity type formed in a side portion of the firstsemiconductor region, wherein a resistivity of the second impurityregion is substantially equal to or smaller than that of the firstimpurity region.

Note that the transistor characteristics can be significantly improvedover the conventional techniques if the implantation dose of the secondimpurity region formed in a side portion of the first semiconductorregion having an upper surface and a side surface, i.e., the fin-shapedsemiconductor region, is about 80% (more preferably 90%) or more of thatof the first impurity region formed in an upper portion of thefin-shaped semiconductor region.

If “the height of the side surface of the fin-shaped semiconductorregion”/“the width of the upper surface of the fin-shaped semiconductorregion in the gate width direction” (hereinafter referred to as the“aspect ratio”) is small, there will be little degradation in thetransistor characteristics even if the implantation dose of the secondimpurity region is somewhat smaller than that of the first impurityregion. An increase in the aspect ratio accordingly increases thenecessity to make the implantation dose of the second impurity region tobe substantially equal to or greater than that of the first impurityregion.

In the first semiconductor device of the present invention, the junctiondepth of the second impurity region may be substantially equal to orgreater than that of the first impurity region.

In the first semiconductor device of the present invention, the firstsemiconductor region may have a fin shape.

In the first semiconductor device of the present invention, the firstsemiconductor region may be formed on an insulating layer formed on thesupporting substrate.

If the first semiconductor device of the present invention furtherincludes: a gate insulating film formed at least on a side surface ofthe first semiconductor region in a predetermined portion of the firstsemiconductor region; and a gate electrode formed on the gate insulatingfilm, wherein the first impurity region and the second impurity regionare formed in another portion of the first semiconductor region otherthan the predetermined portion, it is possible to form a fin-shaped FET.In such a case, the gate insulating film may also be formed on an uppersurface of the first semiconductor region in the predetermined portionof the first semiconductor region. The first impurity region and thesecond impurity region may be a P-type extension region. Thesemiconductor device may further include: an insulative sidewall spacerformed on a side surface of the gate electrode; a third impurity regionof a first conductivity type formed in an upper portion of the firstsemiconductor region; and a fourth impurity region of a firstconductivity type formed in a side portion of the first semiconductorregion, wherein: the third impurity region and the fourth impurityregion may be formed in a portion of the first semiconductor regionwhich is located outside of the insulative sidewall spacer and isprovided in the other portion of the first semiconductor region; and aresistivity of the fourth impurity region may be substantially equal toor smaller than that of the third impurity region. Then, the thirdimpurity region and the fourth impurity region may be a P-typesource-drain region. Alternatively, the semiconductor device may furtherinclude an insulative sidewall spacer formed on a side surface of thegate electrode, wherein the first impurity region and the secondimpurity region are formed in a portion of the first semiconductorregion which is located outside of the insulative sidewall spacer and isprovided in the other portion of the first semiconductor region. Then,the first impurity region and the second impurity region may be a P-typesource-drain region. In these cases, if the height of the side surfaceof the first semiconductor region is greater than the width of the uppersurface of the first semiconductor region in the gate width direction,the effects of the present invention are pronounced.

A second semiconductor device of the present invention includes: aplurality of semiconductor regions formed on a supporting substrate andeach having an upper surface and a side surface; a first impurity regionof a first conductivity type formed in an upper portion of each of theplurality of semiconductor regions; and a second impurity region of afirst conductivity type formed in a side portion of each of theplurality of semiconductor regions, wherein a resistivity of the secondimpurity region is substantially equal to or smaller than that of thefirst impurity region.

If the second semiconductor device of the present invention furtherincludes a gate electrode formed on each of the plurality ofsemiconductor regions with a gate insulating film interposedtherebetween, wherein the gate electrode extends across the plurality ofsemiconductor regions in a gate width direction, it is possible to forma fin-shaped FET. Then, the first impurity region and the secondimpurity region may be a P-type extension region or a P-typesource-drain region.

The second semiconductor device of the present invention may furtherinclude a third semiconductor region connecting together end portions ofthe plurality of semiconductor regions on each side of the semiconductorregions in a gate length direction.

The present invention also relates to a method for producing the firstor second semiconductor device discussed above. The method includes: astep (a) of forming on a supporting substrate a first semiconductorregion having an upper surface and a side surface; and a step (b) ofimplanting the first semiconductor region with an impurity of a firstconductivity type by a plasma doping method to thereby form a firstimpurity region in an upper portion of the first semiconductor regionand a second impurity region in a side portion of the firstsemiconductor region, wherein in the step (b), a plasma doping method iscarried out under a first condition such that an implantation dose isequal to a first dose, and then a plasma doping method is carried outunder a second condition such that the implantation dose is equal to asecond dose smaller than the first dose.

Thus, the method for producing a semiconductor device of the presentinvention is characterized in the control of the implantation dose usinga plasma doping method, and it is possible to control the sheetresistance to a desirable value through the control of the implantationdose by annealing after doping.

Specifically, in plasma doping, as a material gas is supplied into aplasma, there will be radicals, ions or constituent molecules of thematerial gas or molecules or atoms resulting from the decomposition ofthe molecules in the plasma. The present invention focuses on thefollowing inherent properties (1)-(3) of the ions, gas molecules,radicals, etc.:

(1) ions in a plasma are basically incident on the substrate verticallywith respect to the principle plane of the substrate;

(2) neutral species such as gas molecules, radicals, etc., in a plasmaare incident on the substrate in random directions with respect to theprinciple plane of the substrate; and

(3) there is substantially no influence of an impurity desorbed bysputtering on the side surface of the semiconductor region.

In addition to the properties (1)-(3), the present inventors have newlyfound the following property characteristic of plasma doping usingdifferent conditions:

(4) the level of the implantation dose, i.e., the sheet resistance,which is determined as the influence of doping and the influence ofsputtering come to an equilibrium on the semiconductor region uppersurface when plasma doping is performed using different conditions,depends only on the plasma doping conditions at the final stage but noton conditions at intermediate stages.

The present invention also relates to a method for applying this to athree-dimensional device such as a fin-shaped FET, and one primarycharacteristic of the present invention is that “after a plasma dopingmethod is carried out under a first condition such that the implantationdose is equal to a first dose, a plasma doping method is carried outunder a second condition such that the implantation dose is equal to asecond dose smaller than the first dose”. Thus, while the implantationdose of the upper portion of the semiconductor region is basicallydefined by the low-dose second condition, the implantation dose of theside portion of the semiconductor region is basically defined by thehigh-dose first condition. Therefore, it is possible to obtain asemiconductor device including, in a side portion of the semiconductorregion, an impurity region whose implantation dose is substantiallyequal to or greater than that in an upper portion of the semiconductorregion. In other words, it is possible to obtain a semiconductor deviceincluding a low-sheet resistance impurity region in a side portion ofthe semiconductor region. Therefore, it is possible to obtain desirabletransistor characteristics even if the proportion of the width of theimpurity region formed in the side portion of the fin-shapedsemiconductor region increases with respect to the width in the gatewidth direction of the extension region and the source-drain region of afin-shaped FET, for example.

In the method for producing a semiconductor device of the presentinvention, if the step (b) is performed by using a plasma generated froma gas containing the impurity; and a concentration of the gas under thefirst condition is higher than that of the gas under the secondcondition, it is possible to reliably make the implantation dose underthe second condition to be smaller than that under the first condition.

In the method for producing a semiconductor device of the presentinvention, if after the step (b), an implantation dose of the secondimpurity region is substantially equal to or greater than animplantation dose of the first impurity region, it is possible toreliably obtain the effects as set forth above.

The method for producing a semiconductor device of the present inventionmay further include, before the step (a), a step of forming aninsulating layer on the supporting substrate, wherein the firstsemiconductor region is formed on the insulating layer in the step (a).

In the method for producing a semiconductor device of the presentinvention, the side surface of the first semiconductor region may be asurface perpendicular to the upper surface of the first semiconductorregion.

In the method for producing a semiconductor device of the presentinvention, in the first impurity region, an implantation dose at a pointin time when the plasma doping method is carried out under the secondcondition may be decreased from that at a point in time when the plasmadoping method is carried out under the first condition.

In the method for producing a semiconductor device of the presentinvention, the step (b) may be performed by using a plasma generatedfrom a gas containing the impurity; and the gas containing the impuritymay contain molecules B_(m)H_(n) (m and n are natural numbers) composedof boron atoms and hydrogen atoms.

In the method for producing a semiconductor device of the presentinvention, the step (b) may be performed by using a plasma generatedfrom a gas containing the impurity; and the gas containing the impuritymay be a gas obtained by diluting molecules including boron atoms with arare gas.

In the method for producing a semiconductor device of the presentinvention, the step (b) may be performed by using a plasma generatedfrom a gas containing the impurity; and a gas containing the impuritymay be a gas obtained by diluting molecules including the impurity withhelium.

In the method for producing a semiconductor device of the presentinvention, the step (b) may be performed by using a plasma generatedfrom a gas containing the impurity; and the gas containing the impuritymay be a mixed gas of B₂H₆ and He. In such a case, if a concentration bymass of B₂H₆ in the mixed gas is greater than or equal to 0.01% and lessthan or equal to 1%, it is possible to easily introduce boron into thefirst semiconductor region. If the B₂H₆ gas concentration is less than0.01%, it is difficult to introduce a sufficient amount of boron, and ifthe B₂H₆ gas concentration is greater than 1%, a boron-containingdeposit is likely to deposit on the substrate surface.

In the method for producing a semiconductor device of the presentinvention, the step (b) may be performed by using a plasma generatedfrom a gas containing the impurity; and the gas containing the impuritymay contain BF₃, AsH₄ or PH₃.

The method for producing a semiconductor device of the present inventionmay further include, before the step (b), a step of implanting asemiconductor region which is similar to the first semiconductor regionand is provided in each of a plurality of dummy substrates with theimpurity by a plasma doping method under various conditions, so as toidentify, as the first condition, a condition under which a sheetresistance of an impurity region formed in a side portion of thesemiconductor region takes an intended value, and so as to identify, asthe second condition, a condition under which a sheet resistance of animpurity region formed in an upper portion of the semiconductor regiontakes an intended value.

Another method for producing a semiconductor device of the presentinvention includes a step of implanting a semiconductor region with animpurity of a first conductivity type by a plasma doping method tothereby form an impurity region in the semiconductor region, wherein thestep of forming the impurity region comprises a step (a) of carrying outthe plasma doping method under a first condition such that animplantation dose is equal to a first dose, and after the step (a), astep (b) of carrying out the plasma doping method under a secondcondition such that the implantation dose is equal to a second dosesmaller than the first dose.

With the other method for producing a semiconductor device of thepresent invention, an impurity region having a second dose is formed bycarrying out the plasma doping method under the second condition suchthat the implantation dose is equal to the second dose smaller than thefirst dose after carrying out the plasma doping method under the firstcondition such that the implantation dose is equal to the first dose. Ascompared with a case where the impurity region is formed by carrying outthe plasma doping method with only the second condition such that thesecond dose is achieved, it is possible to shorten the plasma dopingtime.

A third semiconductor device includes: a first semiconductor regionformed on a supporting substrate and having an upper surface and a sidesurface; a first impurity region of a first conductivity type formed inan upper portion of the first semiconductor region; and a secondimpurity region of a first conductivity type formed in a side portion ofthe first semiconductor region, wherein a sheet resistance of the secondimpurity region is substantially equal to or smaller than that of thefirst impurity region.

A fourth semiconductor device includes: a first semiconductor regionformed on a supporting substrate and having an upper surface and a sidesurface; a first impurity region of a first conductivity type formed inan upper portion of the first semiconductor region; and a secondimpurity region of a first conductivity type formed in a side portion ofthe first semiconductor region, wherein a spreading resistance of thesecond impurity region is substantially equal to or smaller than that ofthe first impurity region.

EFFECTS OF THE INVENTION

According to the present invention, it is possible to obtain asemiconductor device including an impurity region in a side portion of afin-shaped semiconductor region, the impurity region having animplantation dose substantially equal to or greater than that in anupper portion of the fin-shaped semiconductor region. In other words, itis possible to obtain a semiconductor device including an impurityregion having a low sheet resistance in a side portion of the fin-shapedsemiconductor region. Therefore, it is possible to prevent thedegradation in the characteristics of a three-dimensional device such asa fin-shaped FET.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1D show a structure of a semiconductor device accordingto the first embodiment of the present invention, wherein FIG. 1A is aplan view of a portion of a first embodiment of the fin-shaped FET, FIG.1B is a cross-sectional view along line A-A in FIG. 1A, FIG. 1C is across-sectional view along line B-B in FIG. 1A, and FIG. 1D is across-sectional view taken along line C-C in FIG. 1A.

FIG. 2A to FIG. 2E are cross-sectional views showing, step by step, themethod for producing a semiconductor device according to the firstembodiment of the present invention.

FIG. 3A is a cross-sectional view illustrating a method for doping underthe first plasma doping condition shown in FIG. 2C, and FIG. 3B is across-sectional view illustrating a method for doping under the secondplasma doping condition shown in FIG. 2D.

FIG. 4 shows the relationship between the sheet resistance and theplasma doping time for the first impurity region formed in the upperportion of the fin-shaped semiconductor region in the method forproducing a semiconductor device according to the first embodiment ofthe present invention.

FIG. 5 shows the relationship between the sheet resistance and theplasma doping time for the second impurity region formed in the sideportion of the fin-shaped semiconductor region in the method forproducing a semiconductor device according to the first embodiment ofthe present invention.

FIG. 6 shows the relationship between the sheet resistance and theplasma doping time for each of the first impurity region formed in theupper portion of the fin-shaped semiconductor region and the secondimpurity region formed in the side portion of the fin-shapedsemiconductor region in the method for producing a semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 7 shows the relationship between the sheet resistance and theplasma doping time for the first impurity region formed in the upperportion of the fin-shaped semiconductor region in the first example ofthe method for producing a semiconductor device according to the firstembodiment of the present invention.

FIG. 8 shows the relationship between the sheet resistance and theplasma doping time for the first impurity region formed in the upperportion of the fin-shaped semiconductor region in the second example ofthe method for producing a semiconductor device according to the firstembodiment of the present invention.

FIG. 9 shows the relationship between the sheet resistance and theplasma doping time for the first impurity region formed in the upperportion of the fin-shaped semiconductor region in the third example ofthe method for producing a semiconductor device according to the firstembodiment of the present invention.

FIG. 10 is a plan view of a portion of a fin-shaped FET according to afirst variation of the first embodiment of the present invention.

FIG. 11A to FIG. 11C show cross-sectional structures of thesemiconductor device according to the second variation of the firstembodiment of the present invention, wherein FIG. 11A is across-sectional view taken along line A-A in FIG. 1A, FIG. 11B is across-sectional view taken along line B-B in FIG. 1A, and FIG. 11C is across-sectional view taken along line C-C in FIG. 1A.

FIG. 12 is a flow chart showing the method for determining the plasmadoping condition in the method for producing a semiconductor deviceaccording to a second embodiment of the present invention.

FIG. 13A shows a schematic cross-sectional structure of a dummysubstrate used in the method for determining the plasma doping conditionin the method for producing a semiconductor device according to thesecond embodiment of the present invention, and FIG. 13B shows therelationship between the plasma doping time in step S102 in FIG. 12 andthe sheet resistance.

FIG. 14 shows the relationship between the plasma doping time in stepS103 in FIG. 12 and the sheet resistance.

FIG. 15 shows the relationship between the plasma doping time in stepsS105 and S106 in FIG. 12 and the sheet resistance.

FIG. 16A to FIG. 16D show a structure of a conventional fin-shaped FET,wherein FIG. 16A is a plan view, FIG. 16B is a cross-sectional viewtaken along line A-A in FIG. 16A, FIG. 16C is a cross-sectional viewtaken along line B-B in FIG. 16A, and FIG. 16D is a cross-sectional viewtaken along line C-C in FIG. 16A.

FIG. 17A to FIG. 17D are cross-sectional views o showing, step by step,a conventional method for producing a semiconductor device.

FIG. 18A is a cross-sectional view showing the step of forming asource-drain region of a fin-shaped FET as described in Patent Document1, and FIG. 18B is a cross-sectional view showing the step of forming asource-drain region of a fin-shaped FET as described in Non-PatentDocument 1.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The structure of a semiconductor device according to a first embodimentof the present invention will now be described with reference to thedrawings.

FIG. 1A to FIG. 1D show a structure of a semiconductor device accordingto the first embodiment of the present invention, i.e., a semiconductordevice including a fin-shaped FET, wherein FIG. 1A is a plan view of aportion of the device, FIG. 1B is a cross-sectional view taken alongline A-A in FIG. 1A, FIG. 1C is a cross-sectional view taken along lineB-B in FIG. 1A, and FIG. 1D is a cross-sectional view taken along lineC-C in FIG. 1A.

As shown in FIG. 1A to FIG. 1D, the fin-shaped FET of the presentembodiment includes a supporting substrate 11 made of silicon, forexample, an insulating layer 12 made of silicon oxide, for example,formed on the supporting substrate 11, fin-shaped semiconductor regions13 a to 13 d formed on the insulating layer 12, a gate electrode 15formed on the fin-shaped semiconductor regions 13 a to 13 d with gateinsulating films 14 a to 14 d made of a silicon oxynitride film, forexample, interposed therebetween, insulative sidewall spacers 16 formedon the side surfaces of the gate electrode 15, extension regions 17formed in opposing side regions of the fin-shaped semiconductor regions13 a to 13 d that are opposing each other with the gate electrode 15interposed therebetween, and source-drain regions 27 formed in opposingside regions of the fin-shaped semiconductor regions 13 a to 13 d thatare opposing each other with the gate electrode 15 and the insulativesidewall spacers 16 interposed therebetween. The fin-shapedsemiconductor regions 13 a to 13 d each have a width a in the gate widthdirection of about 30 nm, for example, a width b in the gate lengthdirection of about 200 nm, for example, and a height (thickness) c ofabout 50 nm, for example, and are arranged with a pitch d (about 60 nm,for example) in the gate width direction on the insulating layer 12. Theupper surface and the side surface of the fin-shaped semiconductorregions 13 a to 13 d may or may not be perpendicular to each other. Thegate electrode 15 is formed so as to extend across the fin-shapedsemiconductor regions 13 a to 13 d in the gate width direction. Theextension region 17 includes a first impurity region 17 a formed in anupper portion of each of the fin-shaped semiconductor regions 13 a to 13d, and a second impurity region 17 b formed in a side portion of each ofthe fin-shaped semiconductor regions 13 a to 13 d. The source-drainregion 27 includes a third impurity region 27 a formed in an upperportion of each of the fin-shaped semiconductor regions 13 a to 13 d,and a fourth impurity region 27 b formed in a side portion of each ofthe fin-shaped semiconductor regions 13 a to 13 d. Note that pocketregions are not described herein or shown in the figure.

The characteristics of the present embodiment are as follows. That is,the implantation dose of the second impurity region 17 b formed in theside portion of the fin-shaped semiconductor region is set to besubstantially equal to or greater than that of the first impurity region17 a formed in the upper portion of the fin-shaped semiconductor region.Thus, the sheet resistance of the second impurity region 17 b of theextension region 17 can be set to be less than or equal to that of thefirst impurity region 17 a, whereby it is possible to obtain desirabletransistor characteristics even if the proportion of the width of thesecond impurity region 17 b formed in the side portion of the fin-shapedsemiconductor region increases with respect to the width in the gatewidth direction of the extension region 17. Similarly, the implantationdose of the fourth impurity region 27 b formed in the side portion ofthe fin-shaped semiconductor region is set to be substantially equal toor greater than that of the third impurity region 27 a formed in theupper portion of the fin-shaped semiconductor region. Thus, the sheetresistance of the fourth impurity region 27 b of the source-drain region27 can be set to be less than or equal to that of the third impurityregion 27 a, whereby it is possible to obtain desirable transistorcharacteristics even if the proportion of the width of the fourthimpurity region 27 b formed in the side portion of the fin-shapedsemiconductor region increases with respect to the width in the gatewidth direction of the source-drain region 27.

Though the sheet resistance of the second impurity region 17 b (thefourth impurity region 27 b) is set equal to or smaller than that of thefirst impurity region 17 a (the third impurity region 27 a) in the abovedescription, the same effects can be obtained even when the resistivityor the spreading resistance of the second impurity region 17 b (thefourth impurity region 27 b) is set equal to or smaller than theresistivity or the spreading resistance of the first impurity region 17a (the third impurity region 27 a). Specifically, Rs=ρ/t is satisfiedwhere Rs is a sheet resistance of a target, ρ is a specific resistance(resistivity), t is a thickness (junction depth), and ρw is a spreadingresistance. Further, proportion of Rs to ρw/t is lead since the specificresistance (resistivity) ρ and the spreading resistance ρw are basicallyin one to one correspondence. In the following description, the term,“sheet resistance” is used mainly, but the “sheet resistance” may beread as “resistivity” or “spreading resistance” in description of themagnitude relationship of the resistance.

Note that in the present embodiment, if the implantation dose of thesecond impurity region 17 b formed in the side portion of the fin-shapedsemiconductor region is about 80% (more preferably 90%) or more of thatof the first impurity region 17 a formed in the upper portion of thefin-shaped semiconductor region, the transistor characteristics can besignificantly improved over the conventional techniques. Similarly, ifthe implantation dose of the fourth impurity region 27 b formed in theside portion of the fin-shaped semiconductor region is about 80% (morepreferably 90%) or more of that of the third impurity region 27 a formedin the upper portion of the fin-shaped semiconductor region, thetransistor characteristics can be significantly improved over theconventional techniques.

Moreover, in the present embodiment, if “the height of the side surfaceof the fin-shaped semiconductor region”/“the width of the upper surfaceof the fin-shaped semiconductor region in the gate width direction”(hereinafter referred to as the “aspect ratio”) is small, there will belittle degradation in the transistor characteristics (e.g., draincurrent) even if the implantation dose of the second impurity region 17b is somewhat smaller than that of the first impurity region 17 a,namely, even if the sheet resistance, the resistivity, or the spreadingresistance of the second impurity region 17 b is somewhat larger (about10%, for example) than the sheet resistance, the resistivity, or thespreading resistance of the first impurity region 17 a. An increase inthe aspect ratio accordingly increases the necessity to make theimplantation dose of the second impurity region 17 b to be substantiallyequal to or greater than that of the first impurity region 17 a, thatis, the necessity to set the sheet resistance, the resistivity, or thespreading resistance of the second impurity region 17 b to be equal toor smaller than the sheet resistance, the resistivity, or the spreadingresistance of the first impurity region 17 a. Similarly, if the aspectratio is small, there will be little degradation in the transistorcharacteristics even if the implantation dose of the fourth impurityregion 27 b is somewhat smaller than that of the third impurity region27 a, namely, even if the sheet resistance, the resistivity, or thespreading resistance of the fourth impurity region 27 b is somewhatlarger (about 10%, for example) than the sheet resistance, theresistivity, or the spreading resistance of the third impurity region 27a. An increase in the aspect ratio accordingly increases the necessityto make the implantation dose of the fourth impurity region 27 b to besubstantially equal to or greater than that of the third impurity region27 a, that is, the necessity to set the sheet resistance, theresistivity, or the spreading resistance of the fourth impurity region27 b to be equal or smaller than the sheet resistance, the resistivity,or the spreading resistance of the third impurity region 27 a.

It is noted that with regard to the above-noted characteristic of draincurrent, as the amount of the drain current is dependent on the dose ineach of the three sides of the Fin-shaped semiconductor region, even ifthe width of the top region 17 a becomes smaller relative to the sideregions 17 b, a large drain current may be obtained due to the largeside regions 17 b.

A method for producing a semiconductor device according to the firstembodiment of the present invention will now be described with referenceto the drawings.

FIG. 2A to FIG. 2E are cross-sectional views showing, step by step, themethod for producing a semiconductor device of the first embodiment.Note that FIG. 2A to FIG. 2E correspond to the cross-sectional structuretaken along line C-C in FIG. 1A. In FIG. 2A to FIG. 2E, like elements tothose shown in FIG. 1A to FIG. 1D are denoted by like reference numeralsand will not be described redundantly. It is noted that the thicknessand width dimensions set forth in the following examples are approximatevalues and are intended to be exemplary. As would be understood by thoseskilled in the art, the various components may have differentdimensions.

First, as shown in FIG. 2A, there is provided an SOI substrate, in whichthe insulating layer 12 having a thickness of 150 nm and made of siliconoxide, for example, is provided on the supporting substrate 11 having athickness of 800 μm and made of silicon, for example, and asemiconductor layer having a thickness of 50 nm and made of silicon, forexample, is provided on the insulating layer 12. Then, the semiconductorlayer is patterned to form the n-type fin-shaped semiconductor region 13b to be the active region. The fin-shaped semiconductor region 13 b hasa width a in the gate width direction of about 30 nm, for example, awidth b in the gate length direction of about 200 nm, for example, and aheight (thickness) c of about 50 nm, for example, and is arranged, withother adjacent fin-shaped semiconductor regions, with a pitch d (about60 nm, for example) in the gate width direction on the insulating layer12.

Next, as shown in FIG. 2B, the gate insulating film 14 having athickness of 3 nm and made of a silicon oxynitride film, for example, isformed on the surface of the fin-shaped semiconductor region 13 b, and apolysilicon film 15A having a thickness of 60 nm, for example, is formedacross the entire surface of the supporting substrate 11.

Then, as shown in FIG. 2C, the polysilicon film 15A and the gateinsulating film 14 are etched successively to form the gate electrode 15having a width in the gate length direction of 60 nm, for example, onthe fin-shaped semiconductor region 13 b with the gate insulating film14 b interposed therebetween. Then, using the gate electrode 15 as amask, the fin-shaped semiconductor region 13 b is doped with a p-typeimpurity under a first plasma doping condition (the first condition).Thus, there is formed a p-type extension region 7 including a p-typefirst impurity region 7 a formed in the upper portion of the fin-shapedsemiconductor region 13 b and a p-type second impurity region 7 b formedin the side portion of the fin-shaped semiconductor region 13 b. Theformation is done so that the implantation dose of the first impurityregion 7 a is greater than that of the second impurity region 7 b.Herein, the first plasma doping condition is such that the material gasis B₂H₆ (diborane) diluted with He (helium), the B₂H₆ concentration inthe material gas is 0.05% by mass, the total flow rate of the materialgas is 420 cm³/min (standard state), the chamber pressure is 0.9 Pa, thesource power (the plasma-generating high-frequency power) is 2000 W, thebias power (the high-frequency power applied to the substrate holder) is135 W, and the substrate temperature is 20° C.

Plasma doping is performed for 120 seconds, for example, under the firstplasma doping condition as described above, and then, continuouslywithout turning OFF the discharge, the fin-shaped semiconductor region13 b is doped with a p-type impurity for 680 seconds, for example, underthe second plasma doping condition (the second condition). Thus, asshown in FIG. 2D, there is formed a p-type extension region 17 includingthe p-type first impurity region 17 a formed in the upper portion of thefin-shaped semiconductor region 13 b and the p-type second impurityregion 17 b formed in the side portion of the fin-shaped semiconductorregion 13 b. Thus, the extension region 7 formed in the step shown inFIG. 2C is altered into the extension region 17 in the step shown inFIG. 2D. The formation is done so that the implantation dose of thesecond impurity region 17 b is substantially equal to or greater thanthat of the first impurity region 17 a. Accordingly, the second impurityregion 17 b can be formed so that the sheet resistance, the resistivity,or the spreading resistance of the second impurity region 17 b is equalto or smaller than the sheet resistance, the resistivity, or thespreading resistance of the first impurity region 17 a. Herein, thesecond plasma doping condition is such that the material gas is B₂H₆diluted with He, the B₂H₆ concentration in the material gas is 0.02% bymass, the total flow rate of the material gas is 300 cm³/min (standardstate), the chamber pressure is 0.9 Pa, the source power is 2000 W, thebias power is 135 W, and the substrate temperature is 20° C. Then, usingthe gate electrode 15 as a mask, the fin-shaped semiconductor region 13b is ion-implanted with an impurity to form an n-type pocket region (notshown).

Next, as shown in FIG. 2E, an insulating film having a thickness of 60nm, for example, is formed across the entire surface of the supportingsubstrate 11, and then the insulating film is etched back by usinganisotropic dry etching to thereby form the insulative sidewall spacer16 on the side surface of the gate electrode 15. Then, using the gateelectrode 15 and the insulative sidewall spacer 16 as a mask, thefin-shaped semiconductor region 13 b is doped with a p-type impurity for120 seconds, for example, under the third plasma doping condition (thethird condition), and then, continuously without turning OFF thedischarge, the fin-shaped semiconductor region 13 b is doped with ap-type impurity for 680 seconds, for example, under the fourth plasmadoping condition (the fourth condition). Thus, there is formed thep-type source-drain region 27 including the p-type third impurity region27 a formed in the upper portion of the fin-shaped semiconductor region13 b and the p-type fourth impurity region 27 b formed in the sideportion of the fin-shaped semiconductor region 13 b. When doping underthe third plasma doping condition is performed, the third impurityregion 27 a is formed so that the implantation dose thereof is greaterthan that of the fourth impurity region 27 b. However, by performingdoping under the fourth plasma doping condition where the implantationdose is smaller than that of the third plasma doping condition, thesource-drain region formed by the third plasma doping condition isaltered into the source-drain region 27 by the fourth plasma dopingcondition. The formation is done so that the implantation dose of thefourth impurity region 27 b is substantially equal to or greater thanthat of the third impurity region 27 a. Accordingly, the fourth impurityregion 27 b can be formed so that the sheet resistance, the resistivity,or the spreading resistance of the fourth impurity region 27 b is equalto or smaller than the sheet resistance, the resistivity, or thespreading resistance of the third impurity region 27 a. Note that inorder to make the implantation dose of the third condition greater thanthat of the fourth condition, the B₂H₆ concentration in the material gasand the total flow rate of the material gas of the third condition aremade greater than those of the fourth condition.

The characteristics of the present embodiment are as follows. That is,when the extension region 17 of the fin-shaped FET is formed by using aplasma doping method, the first condition including a relatively largeimplantation dose and the second condition including a relatively smallimplantation dose are used. Thus, it is possible to obtain a fin-shapedMISFET including the extension region 17 in which the implantation doseof the second impurity region 17 b formed in the side portion of thefin-shaped semiconductor region 13 b is substantially equal to orgreater than that of the first impurity region 17 a formed in the upperportion of the fin-shaped semiconductor region 13 b. Therefore, thesheet resistance of the second impurity region 17 b can be set to beless than or equal to that of the first impurity region 17 a, whereby itis possible to obtain desirable transistor characteristics even if theproportion of the width of the second impurity region 17 b formed in theside portion of the fin-shaped semiconductor region increases withrespect to the width in the gate width direction of the extension region17. Similarly, when the source-drain region 27 of the fin-shaped FET isformed by using a plasma doping method, the third condition including arelatively large implantation dose and the fourth condition including arelatively small implantation dose are used. Thus, it is possible toobtain a fin-shaped MISFET including the source-drain region 27 in whichthe implantation dose of the fourth impurity region 27 b formed in theside portion of the fin-shaped semiconductor region 13 b issubstantially equal to or greater than that of the third impurity region27 a formed in the upper portion of the fin-shaped semiconductor region13 b. Therefore, the sheet resistance of the fourth impurity region 27 bcan be set to be less than or equal to that of the third impurity region27 a, whereby it is possible to obtain desirable transistorcharacteristics even if the proportion of the width of the fourthimpurity region 27 b formed in the side portion of the fin-shapedsemiconductor region increases with respect to the width in the gatewidth direction of the source-drain region 27.

In the present embodiment, the n-type fin-shaped semiconductor region 13b is plasma-doped with a p-type impurity to form the p-type extensionregion 17 and the p-type source-drain region 27, i.e., a p-type MISFET.Alternatively, a p-type fin-shaped semiconductor region may be dopedwith an n-type impurity to form an n-type extension region and an n-typesource-drain region, i.e., an n-type MISFET.

Moreover, in the present embodiment, in order to realize a largerimplantation dose for the first condition (the third condition), theB₂H₆ concentration in the material gas and the total flow rate of thematerial gas of the first condition (the third condition) are set to begreater than those of the second condition (the fourth condition).Alternatively, only one of these two of the first condition (the thirdcondition) may be set to be greater than that of the second condition(the fourth condition). Moreover, it is understood that other parameterssuch as the chamber pressure, the source power or the bias power may becontrolled so as to realize a larger implantation dose for the firstcondition (the third condition).

Moreover, in the present embodiment, in order to reduce the sheetresistance of the second impurity region 17 b, it is preferred that thejunction depth of the second impurity region 17 b is set to besubstantially equal to or greater than the junction depth of the firstimpurity region 17 a. Such a configuration can be realized by, forexample, performing appropriate annealing after performing plasma dopingso that the implantation dose of the second impurity region 17 b formedin the side portion of the fin-shaped semiconductor region is greaterthan that of the first impurity region 17 a formed in the upper portionof the fin-shaped semiconductor region. Similarly, in order to reducethe sheet resistance of the fourth impurity region 27 b, it is preferredthat the junction depth of the fourth impurity region 27 b is set to besubstantially equal to or greater than that of the third impurity region27 a. Such a configuration can be realized by, for example, performingappropriate annealing after performing plasma doping so that theimplantation dose of the fourth impurity region 27 b formed in the sideportion of the fin-shaped semiconductor region is greater than that ofthe third impurity region 27 a formed in the upper portion of thefin-shaped semiconductor region.

While B₂H₆ diluted with He is used as the material gas of plasma dopingin the present embodiment, the material gas is not limited to anyparticular gas as long as the gas contains the impurity to be implantedinto the fin-shaped semiconductor regions. Instead of B₂H₆, one mayemploy, for example, other molecules containing boron atoms (e.g., BF₃),other molecules composed of boron atoms and hydrogen atoms, or AsH₄,PH₃, or the like. A gas containing an impurity may or may not be dilutedwith a rare gas such as He. Note that where B₂H₆ diluted with He is usedas the material gas of plasma doping as in the present embodiment, it ispreferred that the concentration by mass of B₂H₆ in the material gas isgreater than or equal to 0.01% and less than or equal to 1%. Then, it ispossible to easily introduce boron into the fin-shaped semiconductorregions. If the B₂H₆ gas concentration is less than 0.01%, it isdifficult to introduce a sufficient amount of boron, and if the B₂H₆ gasconcentration is greater than 1%, a boron-containing deposit is likelyto deposit on the substrate surface.

The mechanism of the present invention will now be described, using theextension region 17 as an example, with reference to the drawings,separately for the upper portion and the side portion of the fin-shapedsemiconductor regions.

(Mechanism of Present Invention)

FIG. 3A is a cross-sectional view of an important part, illustrating amethod for doping under the first plasma doping condition shown in FIG.2C, and FIG. 3B is a cross-sectional view of an important part,illustrating a method for doping under the second plasma dopingcondition shown in FIG. 2D. Note that FIG. 3A and FIG. 3B correspond tothe cross-sectional structure (before the formation of the insulativesidewall spacer 16) taken along line B-B in FIG. 1A. In FIG. 3A and FIG.3B, like elements to those shown in FIG. 1A to FIG. 1D are denoted bylike reference numerals and will not be described redundantly.

FIG. 4 shows the relationship between the sheet resistance and theplasma doping time for the first impurity region formed in the upperportion of the fin-shaped semiconductor region.

FIG. 5 shows the relationship between the sheet resistance and theplasma doping time for the second impurity region formed in the sideportion of the fin-shaped semiconductor region.

FIG. 6 shows the relationship between the sheet resistance and theplasma doping time for each of the first impurity region formed in theupper portion of the fin-shaped semiconductor region and the secondimpurity region formed in the side portion of the fin-shapedsemiconductor region.

Note that the sheet resistance shown in FIG. 4 to FIG. 6 (this appliesalso to FIG. 7 to FIG. 9 to be discussed later) is obtained byperforming RTA (rapid thermal annealing) for 20 seconds at a temperatureof 1075° C. after plasma doping. By performing sufficient annealingafter doping, it is possible to realize a one-to-one correspondencebetween the implantation dose and the sheet resistance.

(Mechanism of Present Invention for Upper Portion of Fin-ShapedSemiconductor Region)

First, as shown in FIG. 3A, the fin-shaped semiconductor regions 13 a to13 d are doped with a p-type impurity under the first plasma dopingcondition (the first condition). Thus, the first impurity region 7 a isformed in the upper portion of the fin-shaped semiconductor regions 13 ato 13 d, wherein the implantation dose of the first impurity region 7 ais dictated by the balance between implanted ions 18 a, an adsorbedspecies (a neutral species such as gas molecules or radicals) 18 b, andan impurity 18 c that is desorbed from the fin-shaped semiconductorregions 13 a to 13 d by sputtering.

As indicated by the broken line in FIG. 4, where the plasma doping timewith only the first condition is elongated, the amount of impurityintroduction by the implanted ions 18 a and the adsorbed species 18 bintroduced into the semiconductor regions 13 a to 13 d is greater thanthe amount of the impurity 18 c desorbed from the fin-shapedsemiconductor regions 13 a to 13 d by sputtering, whereby the sheetresistance of the first impurity region 7 a decreases monotonously, inan initial stage of plasma doping. Then, as the amount of impurityintroduction per unit time into the semiconductor regions 13 a to 13 ddecreases gradually, the degree of decrease in the sheet resistance ofthe first impurity region 7 a also starts becoming more gentle, and thedegree of decrease eventually becomes very gentle. This is because theamount of increase in the amount of impurity introduction per unit timedecreases gradually as the amount of impurity introduced by theimplanted ions 18 a and the adsorbed species 18 b and the amount ofimpurity desorbed by sputtering come to an equilibrium. Therefore, wherean impurity is introduced only under the first condition, the finalsheet resistance of the first impurity region 7 a is the sheetresistance corresponding to the dose implanted into the first impurityregion 7 a by the time when the amount of impurity introduction and theamount of impurity desorption come to an equilibrium under the firstcondition (the “point of equilibrium under first condition” in FIG. 4)(i.e., the sheet resistance at the “point of equilibrium under firstcondition” in FIG. 4).

Then, as shown in FIG. 3B, following the plasma doping under the firstcondition, the fin-shaped semiconductor regions 13 a to 13 d are dopedwith a p-type impurity after switching to the second plasma dopingcondition (the second condition) where the gas concentration is lowerthan that of the first condition. Thus, the first impurity region 17 ais formed in the upper portion of the fin-shaped semiconductor regions13 a to 13 d, wherein the implantation dose of the first impurity region17 a is dictated by the balance between implanted ions 19 a, an adsorbedspecies (a neutral species such as gas molecules or radicals) 19 b, andan impurity 19 c that is desorbed from the fin-shaped semiconductorregions 13 a to 13 d by sputtering. Thus, the first impurity region 7 ashown in FIG. 3A is altered into the first impurity region 17 a as shownin FIG. 3B. Since the gas concentration of the second condition is lowerthan that of the first condition, the implantation dose of the firstimpurity region 17 a decreases from that of the initially-formed firstimpurity region 7 a. In other words, the sheet resistance of the firstimpurity region 17 a becomes higher than that of the first impurityregion 7 a.

As indicated by the solid line in FIG. 4, after the condition isswitched to the second condition where the gas concentration is lowerthan that of the first condition during a plasma doping process, thephenomenon that the impurity is desorbed from the fin-shapedsemiconductor regions by sputtering becomes more pronounced under thesecond condition as compared with the first condition. Therefore, aportion of the impurity having been introduced into the fin-shapedsemiconductor region by the plasma doping under the first condition thatis in excess of the level of the dose implanted by the time when theamount of impurity introduction and the amount of impurity desorptioncome to an equilibrium under the second condition (i.e., the dosecorresponding to the sheet resistance at the “point of equilibrium undersecond condition” in FIG. 4) is desorbed from the fin-shapedsemiconductor regions by sputtering when performing the plasma dopingunder the second condition. In other words, when the condition isswitched from the first condition to the second condition during aplasma doping process, the dose to be eventually introduced into thefin-shaped semiconductor regions is equal to a dose dictated by thebalance between the amount of impurity introduced by the implanted ionsand the adsorbed species and the amount of impurity desorbed bysputtering under the second condition, whereby the implantation dosedecreases and the sheet resistance increases and becomes stable at theincreased level. Specifically, the balance between the amount ofimpurity introduction and the amount of impurity desorption in plasmadoping is dependent only on the doping condition at the final stage (thesecond condition in the present embodiment), but not on the precedingconditions (the first condition in the present embodiment). Thus, thesheet resistance of the first impurity region is at the level at whichthe sheet resistance eventually becomes stable under the secondcondition (the sheet resistance at the “point of equilibrium undersecond condition” in FIG. 4).

As described above, the difference between the case where plasma dopingis performed only with the first condition (the broken line in FIG. 4)and the case where plasma doping is performed with the first conditionand the second condition (the solid line in FIG. 4) corresponds to thedifference between the sheet resistance dictated by the balance betweenthe amount of impurity introduction and the amount of impuritydesorption under the first condition and the sheet resistance dictatedby the balance between the amount of impurity introduction and theamount of impurity desorption under the second condition. Thus, whenplasma doping is performed only with the first condition, the sheetresistance becomes stable at a level that is dictated by the balancebetween the amount of impurity introduction and the amount of impuritydesorption under the first condition, whereas when plasma doping isperformed during which the condition is switched from the firstcondition to the second condition, the sheet resistance becomes stableat a level that is dictated by the balance between the amount ofimpurity introduction and the amount of impurity desorption under thesecond condition. The difference between the sheet resistance with thefirst condition and that with the second condition is due to thedifference therebetween in the influence of doping and sputtering.

(Mechanism of Present Invention for Side Portion of Fin-ShapedSemiconductor Region)

First, as shown in FIG. 3A, the fin-shaped semiconductor regions 13 a to13 d are doped with a p-type impurity under the first plasma dopingcondition (the first condition). Thus, the second impurity region 7 b isformed in the side portion of the fin-shaped semiconductor regions 13 ato 13 d, wherein the implantation dose of the second impurity region 7 bis dictated primarily by the adsorbed species (a neutral species such asgas molecules or radicals) 18 b. In this process, since there are ionsthat are incident on the side surface of the fin-shaped semiconductorregions 13 a to 13 d from an inclined direction, there are present theimplanted ions 18 a and the impurity 18 c that is desorbed from thefin-shaped semiconductor regions 13 a to 13 d by sputtering, butnevertheless the influence thereof is very little as compared with theadsorbed species 18 b and doping by the adsorbed species 18 b will bedominant. Specifically, the number of the implanted ions 18 a doped intothe side portion of the fin-shaped semiconductor regions 13 a to 13 dand the impurity 18 c desorbed from the side portion of the fin-shapedsemiconductor regions 13 a to 13 d by sputtering is very small ascompared with the number of the implanted ions 18 a doped into the upperportion of the fin-shaped semiconductor regions 13 a to 13 d and theimpurity 18 c desorbed from the upper portion of the fin-shapedsemiconductor regions 13 a to 13 d by sputtering.

As indicated by the one-dot chain line in FIG. 5, where the plasmadoping time with only the first condition is elongated, the sheetresistance of the second impurity region 7 b decreases monotonously inan initial stage of plasma doping. Then, as the amount of impurityintroduction per unit time into the semiconductor regions 13 a to 13 ddecreases gradually, the degree of decrease in the sheet resistance ofthe second impurity region 7 b also starts becoming more gentle, and thedegree of decrease eventually becomes very gentle. This is because theamount of increase in the amount of impurity introduction per unit timedecreases gradually as the amount of impurity introduced by theimplanted ions 18 a and the adsorbed species 18 b and the amount ofimpurity desorbed by sputtering come to an equilibrium. However, sincethe dose of the implanted ions 18 a doped into the side portion of thefin-shaped semiconductor regions 13 a to 13 d is smaller than the doseof the implanted ions 18 a doped into the upper portion of thefin-shaped semiconductor regions 13 a to 13 d, the sheet resistance ofthe second impurity region 7 b becomes stable at a higher level than thesheet resistance of the first impurity region 7 a.

Then, as shown in FIG. 3B, following the plasma doping under the firstcondition, the fin-shaped semiconductor regions 13 a to 13 d are dopedwith a p-type impurity after switching to the second plasma dopingcondition (the second condition) where the gas concentration is lowerthan that of the first condition. Thus, the second impurity region 17 bis formed in the side portion of the fin-shaped semiconductor regions 13a to 13 d. In this process, since the amount of the impurity 19 c thatis desorbed from the side portion of the fin-shaped semiconductorregions 13 a to 13 d by sputtering is small, the implantation dose ofthe second impurity region 17 b does not change or decrease onlyslightly from that of the second impurity region 7 b.

Therefore, as indicated by the two-dot chain line in FIG. 5, even if thecondition is switched to the second condition where the gasconcentration is lower than that of the first condition during theplasma doping process, the sheet resistance of the second impurityregion 17 b will be a value close to the sheet resistance immediatelybefore switching to the second condition, i.e., the sheet resistancedictated by the first condition.

As described above, there is little decrease in the implantation dose bysputtering in the side portion of the fin-shaped semiconductor regions13 a to 13 d, whereby the difference between the sheet resistanceobtained when plasma doping is performed with only the first condition(the one-dot chain line in FIG. 5) and that obtained when plasma dopingis performed with the first condition and the second condition (thetwo-dot chain line in FIG. 5) is substantially none or very little if atall.

(Comparison of Mechanism of Present Invention Between Upper Portion andSide Portion of Fin-Shaped Semiconductor Region)

Referring now to FIG. 6, the results of plasma doping performed by usingthe second condition with a lower gas concentration, following plasmadoping using the first condition, for the upper portion of thefin-shaped semiconductor region and those for the side portion of thefin-shaped semiconductor region will be described together. Note that inFIG. 6, the solid line is that in FIG. 4, and the two-dot chain line isthat in FIG. 5.

As indicated by the solid line in FIG. 6, the influence of sputteringduring plasma doping in the first impurity region (the upper portion ofthe semiconductor region) is greater than that in the second impurityregion (the side portion of the semiconductor region), whereby when thecondition is switched from the first condition to the second condition,a portion of the impurity introduced in excess of the implantation dosecorresponding to the level of the sheet resistance dictated by thesecond condition is pushed out of the semiconductor region by sputteringwhen performing plasma doping under the second condition. Therefore, thelevel at which the dose introduced by ion implantation and adsorption ofthe neutral species (such as gas molecules or radicals) and the amountof impurity desorbed from the semiconductor region by sputtering come toan equilibrium depends only on the final one of a plurality of plasmadoping conditions used, but not on the preceding plasma dopingconditions. Therefore, the value of the sheet resistance in the firstimpurity region (the upper portion of the semiconductor region) is atthe level at which the sheet resistance eventually becomes stable underthe second condition.

On the other hand, as indicated by the two-dot chain line in FIG. 6, theinfluence of sputtering during plasma doping in the second impurityregion (the side portion of the semiconductor region) is smaller thanthat in the first impurity region (the upper portion of thesemiconductor region), whereby even when the condition is switched fromthe first condition to the second condition, the dose introduced underthe first condition will not be decreased at all or only slightly if atall by sputtering under the second condition. Therefore, the value ofthe sheet resistance in the second impurity region (the side portion ofthe semiconductor region) will be a value close to the sheet resistanceimmediately before switching to the second condition, i.e., the sheetresistance dictated by the first condition.

Thus, by performing plasma doping while switching the condition from thefirst condition where the implantation dose is relatively large to thesecond condition where the implantation dose is relatively small, theimplantation dose in the first impurity region (the upper portion of thesemiconductor region) and that in the second impurity region (the sideportion of the semiconductor region) can be made equal to each otherwith a very high precision. Moreover, it is possible to make theimplantation dose in the second impurity region (the side portion of thesemiconductor region) larger than that in the first impurity region (theupper portion of the semiconductor region). FIG. 6 shows a processwindow in which the implantation dose of the first impurity region (theupper portion of the semiconductor region) and that in the secondimpurity region (the side portion of the semiconductor region) can bemade equal to each other.

Note that also in the formation of the source-drain region 27, theimplantation dose in the third impurity region (the upper portion of thesemiconductor region) 27 a and that in the fourth impurity region (theside portion of the semiconductor region) 27 b can be made equal to eachother by using a mechanism similar to that for the formation of theextension region 17. Moreover, it is possible to make the implantationdose in the fourth impurity region (the side portion of thesemiconductor region) 27 b larger than that in the third impurity region(the upper portion of the semiconductor region) 27 a.

Specific examples will be used below to illustrate how the value of thesheet resistance in the first impurity region (the upper portion of thesemiconductor region) will be at the level at which the sheet resistanceeventually becomes stable under the second condition.

First Example

First, the first example will be described with reference to FIG. 7.Curve A in FIG. 7 corresponds to the case where plasma doping isperformed only with the first condition as described above with respectto FIG. 4, wherein the plasma doping condition is such that, forexample, the material gas is B₂H₆ diluted with He, the B₂H₆concentration in the material gas is 0.05% by mass, the total flow rateof the material gas is 420 cm³/min (standard state), the chamberpressure is 0.9 Pa, the source power (plasma-generating high-frequencypower) is 2000 W, the bias power (the high-frequency power applied tothe substrate holder) is 135 W, and the substrate temperature is 20° C.Curve B in FIG. 7 corresponds to the case where plasma doping isperformed with only the second condition as described above with respectto FIG. 4, wherein the plasma doping condition is such that, forexample, the material gas is B₂H₆ diluted with He, the B₂H₆concentration in the material gas is 0.02% by mass, the total flow rateof the material gas is 300 cm³/min (standard state), the chamberpressure is 0.9 Pa, the source power (plasma-generating high-frequencypower) is 2000 W, the bias power (the high-frequency power applied tothe substrate holder) is 135 W, and the substrate temperature is 20° C.

Note that in the first example, in order to lower the sheet resistancein the second impurity region (the side portion of the semiconductorregion) dictated by the first condition, the B₂H₆ concentration and thetotal flow rate of the first condition are set to 0.05% by mass and 420cm³/min (standard state), respectively, which are greater than those ofthe second condition.

Moreover, in the first example, the timing at which the condition isswitched from the first condition to the second condition is set to be120 seconds after the start of the plasma doping.

Curve C1 in FIG. 7 shows the change in the sheet resistance of the firstimpurity region (the upper portion of the semiconductor region) obtainedwhen using the first condition from the start of plasma doping until 120seconds later, and then, continuously without turning OFF theplasma-generating discharge, performing plasma doping under the secondcondition (i.e., the change in the sheet resistance of the firstexample). As indicated by Curve C1 in FIG. 7, it can be seen that thesheet resistance monotonously decreases after the start of plasma dopinguntil about 200 seconds later, after which the gradient turns fromnegative to positive, and the sheet resistance is clearly increasingfrom about 200 seconds from the start of the plasma doping until about800 seconds from the start.

Note that in the first example, the smallest value of the sheetresistance at 200 seconds after the start of the plasma doping is147Ω/□, and the increased sheet resistance value at about 800 secondsafter the start of the plasma doping is 171Ω/□, the differencetherebetween being 24Ω/□. The amount of increase in the sheet resistanceis about 15% of the sheet resistance value (170Ω/□) at which the sheetresistance eventually becomes stable when doping with only the secondcondition. It should be noted here that the sheet resistance value171Ω/□ at about 800 seconds after the start of the plasma doping in thefirst example is very close to the sheet resistance value (170Ω/□) atwhich the sheet resistance eventually becomes stable when doping withonly the second condition. It is believed that this means self-alignmentto be described below. That is, it has been confirmed that where thetiming at which the condition is switched from the first condition tothe second condition is set to be relatively late, i.e., 120 secondsafter the start of the plasma doping, even if the sheet resistance isintentionally lowered to be smaller than the target value (170Ω/□ in thepresent example), the final sheet resistance value increases in aself-aligned manner to the sheet resistance value (170Ω/□ in the presentexample) dictated by the second condition, being the latter plasmadoping condition. This is a very special phenomenon unique to thepresent invention. Note that the timing at which the condition isswitched from the first condition to the second condition is set to besubstantially later in the first example in order to clearly illustratethis phenomenon, and it is preferred that the condition is switched fromthe first condition to the second condition at a timing such that thesheet resistance of the second impurity region (the side portion of thesemiconductor region) dictated by the first condition (the level of theminimum value before the condition is switched to the second condition)takes a desirable value.

Second Example

Next, the second example will be described with reference to FIG. 8.

In the first example, the timing at which the condition is switched fromthe first condition to the second condition is set to be 120 secondsafter the start of the plasma doping. In the second example, the timingis changed so that the condition is switched from the first condition tothe second condition 60 seconds after the start of the plasma doping.Note that the plasma doping condition of the first condition and that ofthe second condition are the same as those of the first example, andCurve A and Curve B in FIG. 8 are the same as Curve A and Curve B inFIG. 7.

Curve C2 in FIG. 8 shows the change in the sheet resistance of the firstimpurity region (the upper portion of the semiconductor region) obtainedwhen using the first condition from the start of plasma doping until 60seconds later, and then, continuously without turning OFF theplasma-generating discharge, performing plasma doping under the secondcondition (i.e., the change in the sheet resistance of the secondexample). It should be noted that also in the second example, as in thefirst example, the transition of the sheet resistance shows a tendencythat disproves the common knowledge of conventional plasma doping, asindicated by Curve C2 in FIG. 8.

Specifically, in the conventional plasma doping, the sheet resistancemonotonously decreases over time. This is believed to be as follows.While the doping dose increases as ions from plasma are implanted, asthe adsorption of radicals, gas molecules, etc., advances, and as theadsorbed radicals, gas molecules, etc., are struck by ions from above soas to be pushed into the semiconductor region, the implantation doseincreases as the plasma doping time increases based on these phenomena.Of course the amount of increase in the dose per unit time may varydepending on the plasma doping condition, and the amount of increase inthe dose per unit time may gradually decrease as the influence of dopingand the influence of sputtering come to an equilibrium, but it isnevertheless in the nature of conventional plasma doping that theimplantation dose necessarily increases as the plasma doping timeincreases.

In contrast, in the second example, although the sheet resistancemonotonously decreases as in ordinary plasma doping until 200 secondsafter the start of the plasma doping, the gradient of the change in thesheet resistance turns from negative to positive at about 200 secondsafter the start of the plasma doping. Then, surprisingly, after 200seconds since the start of the plasma doping, the sheet resistancestarted increasing toward the sheet resistance value (170Ω/□) at whichthe sheet resistance eventually becomes stable when doping with only thesecond condition. Then, after the sheet resistance reached the sheetresistance value (170Ω/□) at which the sheet resistance eventuallybecomes stable when doping with only the second condition at about 400seconds after the start of the plasma doping, the rate of increase inthe sheet resistance decreased. Specifically, the sheet resistance at200 seconds after the start of the plasma doping is 163Ω/□, that at 400seconds after the start of the plasma doping is 170Ω/□, and that at 800seconds after the start of the plasma doping is 172Ω/□. It appears fromthese results that the increase in the sheet resistance from 200 secondsto 400 seconds after the start of the plasma doping is the action of anatural mechanism aiming at the sheet resistance value (170Ω/□) at whichthe sheet resistance eventually becomes stable when doping with only thesecond condition. Moreover, as shown in FIG. 8, when obtaining thetarget sheet resistance value (170Ω/□ (including the tolerance range)),it is possible to further shorten the plasma doping time by doping withthe second condition after doping with the first condition, as comparedwith a case where the doping is performed with only the second condition(Curve B).

Note that in FIG. 8, the increase to the target value (170Ω/□ in thepresent example) from the sheet resistance, 163Ω/□, at about 200 secondsafter the start of the plasma doping when the sheet resistance is at thelowest level is about 4% of the target value. This is smaller than theamount of increase of about 15% shown in the first example. Thus, thereis an effect that it is possible to control the amount of increase fromthe sheet resistance value at the lowest level to the sheet resistanceto the target value (e.g., 170Ω/□ in the present example), by adjustingthe timing at which the condition is switched from the first conditionto the second condition. Thus, by controlling the timing is it possibleto suppress/minimize the deviation between the target sheet resistanceand the lowest sheet resistance value.

Third Example

Next, the third example will be described with reference to FIG. 9.

In the second example, the timing at which the condition is switchedfrom the first condition to the second condition is set to be 60 secondsafter the start of the plasma doping. In the third example, the timingis changed so that the condition is switched from the first condition tothe second condition 20 seconds after the start of the plasma doping.Note that the plasma doping condition of the first condition and that ofthe second condition are the same as those of the first example, andCurve A and Curve B in FIG. 9 are the same as Curve A and Curve B inFIG. 7.

Curve C3 in FIG. 9 shows the change in the sheet resistance obtainedwhen using the first condition from the start of plasma doping until 20seconds later, and then, continuously without turning OFF theplasma-generating discharge, performing plasma doping under the secondcondition (i.e., the change in the sheet resistance of the thirdexample). As indicated by Curve C3 in FIG. 9, also in the third examplewhere the timing at which the condition is switched from the firstcondition to the second condition is set to be 20 seconds after thestart of the plasma doping, the sheet resistance value at which thesheet resistance becomes stable between 400 seconds and 800 secondsafter the start of the plasma doping was within a tolerance range of,though slightly higher than, the sheet resistance value (170Ω/□) atwhich the sheet resistance eventually becomes stable when doping withonly the second condition.

As can be seen from the first to third examples described above, thelevel of the implantation dose, i.e., the sheet resistance, which isdetermined as the influence of doping and the influence of sputteringcome to an equilibrium on the semiconductor region upper surface whenplasma doping is performed using different conditions, depends only onthe plasma doping condition at the final stage but not on conditions atintermediate stages. Specifically, an impurity that has once beenintroduced into a semiconductor region can go out of the semiconductorregion under conditions such that the sputtering is dominant.

First Variation of First Embodiment

A structure of a semiconductor device according to a first variation ofthe first embodiment of the present invention will now be described withreference to the drawings.

FIG. 10 is a plan view of a semiconductor device of this variation,specifically, a semiconductor device including a fin-shaped FET. Notethat in FIG. 10, like elements to those of the first embodiment shown inFIG. 1A to FIG. 1D are denoted by like reference numerals.

As shown in FIG. 10, this variation differs from the first embodimentshown in FIG. 1A to FIG. 1D in that other fin-shaped semiconductorregions 13 e and 13 f connect together end portions of the fin-shapedsemiconductor regions 13 a to 13 d on each side of the fin-shapedsemiconductor regions 13 a to 13 d in the gate length direction.

According to this variation, it is possible to form a single fin-shapedFET with the fin-shaped semiconductor regions 13 a to 13 f, whileobtaining effects similar to those of the first embodiment.

Second Variation of First Embodiment

A structure of a semiconductor device according to a second variation ofthe first embodiment of the present invention will now be described withreference to the drawings.

A plan view showing a structure of a semiconductor device of thisvariation, specifically, a semiconductor device including a fin-shapedFET, is the same as FIG. 1A being a plan view of the first embodiment.FIG. 11A to FIG. 1C show cross-sectional structures of the semiconductordevice of this variation, wherein FIG. 11A is a cross-sectional viewtaken along line A-A in FIG. 1A, FIG. 11B is a cross-sectional viewtaken along line B-B in FIG. 1A, and FIG. 11C is a cross-sectional viewtaken along line C-C in FIG. 1A.

As shown in FIG. 11A to FIG. 11C, this variation differs from the firstembodiment shown in FIG. 1A to FIG. 1D as follows. Specifically, in thefirst embodiment, the gate insulating films 14 a to 14 d having athickness of about 3 nm and made of a silicon oxynitride film, forexample, are formed on the upper surface and the side surface of thefin-shaped semiconductor regions 13 a to 13 d. In contrast, in thisvariation, the gate insulating films 14 a to 14 d are formed only on theside surface of the fin-shaped semiconductor regions 13 a to 13 d, andinsulating films 24 a to 24 d having a thickness of 20 nm and made of asilicon oxide film, for example, are formed on the upper surface of thefin-shaped semiconductor regions 13 a to 13 d.

Thus, in this variation, only the side portion of the fin-shapedsemiconductor regions 13 a to 13 d is used as a channel region. Alsowith such a structure, it is possible to obtain effects similar to thoseof the first embodiment if the aspect ratio (“the height of the sidesurface of the fin-shaped semiconductor region”/“the width of the uppersurface of the fin-shaped semiconductor region in the gate widthdirection”) is large.

Second Embodiment

A method for producing a semiconductor device according to a secondembodiment of the present invention, specifically, a method fordetermining the first and second plasma doping conditions in the methodfor producing a semiconductor device of the first embodiment describedabove, will now be described with reference to the drawings.

FIG. 12 is a flow chart showing the method for determining the plasmadoping condition of the present embodiment. FIG. 13A shows a schematiccross-sectional structure of a dummy substrate used in the method fordetermining the plasma doping condition of the present embodiment, andFIG. 13B shows the relationship between the plasma doping time in stepS102 and the sheet resistance. FIG. 14 shows the relationship betweenthe plasma doping time in step S103 and the sheet resistance. FIG. 15shows the relationship between the plasma doping time in steps S105 andS106 and the sheet resistance.

First, in step S101, a plurality of identical dummy substrates 51 areprovided as dummy substrates for use in setting the plasma dopingconditions, and fin-shaped semiconductor regions (hereinafter referredto as “fins”) 52 having the same specifications (or substantially thesame specifications) as those of a device to be produced, e.g., fins 52similar to the fin-shaped semiconductor regions 13 a to 13 d of thefirst embodiment shown in FIG. 1A to FIG. 1D, are formed on each dummysubstrate 51, as shown in FIG. 13A. As shown in FIG. 13A, each fin 52includes a first surface parallel to the principle plane of thesubstrate (on which the point a is the sheet resistance measurementpoint) and a second surface perpendicular to the principle plane of thesubstrate (on which the point b is the sheet resistance measurementpoint).

Then, in step S102, the fins 52 are plasma-doped with a p-type impurityunder various conditions by using the plurality of dummy substrates 51with the fins 52 formed thereon (hereinafter referred to as the “firstPD”). Then, after a heat treatment for activating the implanted impurityis performed, the sheet resistance at the point a of the fins 52 andthat at the point b of the fins 52 are measured. Then, those conditionsunder which the sheet resistance at the point b takes a desirable valueare determined to be the “first PD conditions”. FIG. 13B shows how thesheet resistance at the point b takes a desirable value in step S102. Atthis point, the sheet resistance at the point a is half of that at thepoint b, for example.

Note that where the sheet resistance at the point b is different from adesirable value, step S102 is repeated while changing the plasma dopingconditions using an unprocessed dummy substrate 51 with the fins 52formed thereon until the sheet resistance at the point b is equal to thedesirable value. When there is no longer an unprocessed dummy substrate51 with the fins 52 formed hereon, step S101 and step S102 are repeated.

Then, in step S103, the fins 52 are plasma-doped with a p-type impurityunder various conditions by using a plurality of unprocessed dummysubstrate 51 with the fins 52 formed thereon (hereinafter referred to asthe “second PD”). Then, after a heat treatment for activating theimplanted impurity is performed, the sheet resistance at the point a ofthe fins 52 and that at the point b of the fins 52 are measured. Then,those conditions under which the sheet resistance at the point a takes adesirable value are determined to be the “second PD conditions”. FIG. 14shows how the sheet resistance at the point a takes a desirable value instep S103. At this point, the sheet resistance at the point b is higherthan that at the point a.

Note that where the sheet resistance at the point a is different from adesirable value, step S103 is repeated while changing the plasma dopingconditions using an unprocessed dummy substrate 51 with the fins 52formed thereon until the sheet resistance at the point a is equal to thedesirable value. When there is no longer an unprocessed dummy substrate51 with the fins 52 formed hereon, step S101 and step S103 are repeated.

Then, in step S104, there is formed a substrate for producing a devicethat has been subjected to steps up to immediately before the PDprocess, e.g., a substrate having a structure of the first embodiment asshown in FIG. 2C. The substrate has been subjected to the formation ofthe fins and preliminary steps (e.g., washing) before the PD process.

Then, in step S105, the substrate for producing a device is subjected toplasma doping using the first PD conditions determined in step S102(conditions under which the sheet resistance at the point b takes adesirable value).

Then, in step S106, the substrate for producing a device is subjected toplasma doping using the second PD conditions determined in step S103(conditions under which the sheet resistance at the point a takes adesirable value). In this process, step S106 may be performed in thesame chamber as in step S105 and continuously thereafter without turningOFF the discharge. FIG. 15 shows how the sheet resistance in the upperportion (the point a) of the fins and that in the side portion (thepoint b) of the fins take desirable values in steps S105 and S106. Notethat FIG. 15 shows a case where the sheet resistance in the upperportion (the point a) of the fins and that in the side portion (thepoint b) of the fins are set to the same value.

Finally, in step S107, steps after the PD process, e.g., washing, resistpeeling, heat treatment for activation, etc., are performed to completethe device production.

As described above, according to the present embodiment, it is possibleto reliably produce a semiconductor device having a structure of thefirst embodiment, i.e., a semiconductor device including fin-shapedsemiconductor regions and being capable of exerting desirablecharacteristics.

INDUSTRIAL APPLICABILITY

The present invention relates to a semiconductor device and a method forproducing the same, and more particularly is useful in realizing asemiconductor device of a three-dimensional structure includingfin-shaped semiconductor regions on a substrate with which desirablecharacteristics can be obtained.

1. A semiconductor device, comprising: a first semiconductor regionformed on a substrate and having an upper surface and a side surface; afirst impurity region of a first conductivity type formed in an upperportion of the first semiconductor region; and a second impurity regionof a first conductivity type formed in a side portion of the firstsemiconductor region, wherein a resistivity of the second impurityregion is substantially equal to or smaller than that of the firstimpurity region.
 2. The semiconductor device of claim 1, wherein ajunction depth of the second impurity region is substantially equal toor greater than that of the first impurity region.
 3. The semiconductordevice of claim 1, wherein the first semiconductor region has a finshape.
 4. The semiconductor device of claim 1, wherein the firstsemiconductor region is formed on an insulating layer formed on thesubstrate.
 5. The semiconductor device of claim 1, further comprising: agate insulating film formed at least on a side surface of the firstsemiconductor region in a predetermined portion of the firstsemiconductor region; and a gate electrode formed on the gate insulatingfilm, wherein the first impurity region and the second impurity regionare formed in another portion of the first semiconductor region otherthan the predetermined portion.
 6. The semiconductor device of claim 5,wherein the gate insulating film is formed also on an upper surface ofthe first semiconductor region in the predetermined portion of the firstsemiconductor region.
 7. The semiconductor device of claim 5, whereinthe first impurity region and the second impurity region are a P-typeextension region.
 8. The semiconductor device of claim 5, furthercomprising: an insulative sidewall spacer formed on a side surface ofthe gate electrode; a third impurity region of a first conductivity typeformed in an upper portion of the first semiconductor region; and afourth impurity region of a first conductivity type formed in a sideportion of the first semiconductor region, wherein: the third impurityregion and the fourth impurity region are formed in a portion of thefirst semiconductor region which is located outside of the insulativesidewall spacer and is provided in the other portion of the firstsemiconductor region; and a resistivity of the fourth impurity region issubstantially equal to or smaller than that of the third impurityregion.
 9. The semiconductor device of claim 8, wherein the thirdimpurity region and the fourth impurity region are a P-type source-drainregion.
 10. The semiconductor device of claim 5, further comprising aninsulative sidewall spacer formed on a side surface of the gateelectrode, wherein the first impurity region and the second impurityregion are formed in a portion of the first semiconductor region whichis located outside of the insulative sidewall spacer and is provided inthe other portion of the first semiconductor region.
 11. Thesemiconductor device of claim 5, wherein the first impurity region andthe second impurity region are a P-type source-drain region.
 12. Thesemiconductor device of claim 5, wherein a height of the side surface ofthe first semiconductor region is greater than a width of the uppersurface of the first semiconductor region in a gate width direction. 13.A semiconductor device, comprising: a plurality of semiconductor regionsformed on a substrate and each having an upper surface and a sidesurface; a first impurity region of a first conductivity type formed inan upper portion of each of the plurality of semiconductor regions; anda second impurity region of a first conductivity type formed in a sideportion of each of the plurality of semiconductor regions, wherein aresistivity of the second impurity region is substantially equal to orsmaller than that of the first impurity region.
 14. The semiconductordevice of claim 13, further comprising a gate electrode formed on eachof the plurality of semiconductor regions with a gate insulating filminterposed therebetween, wherein the gate electrode extends across theplurality of semiconductor regions in a gate width direction.
 15. Thesemiconductor device of claim 14, wherein the first impurity region andthe second impurity region are a P-type extension region.
 16. Thesemiconductor device of claim 14, wherein the first impurity region andthe second impurity region are a P-type source-drain region.
 17. Thesemiconductor device of claim 13, further comprising a thirdsemiconductor region connecting together end portions of the pluralityof semiconductor regions on each side of the semiconductor regions in agate length direction.
 18. A method for producing a semiconductordevice, comprising: a step (a) of forming on a substrate a firstsemiconductor region having an upper surface and a side surface; and astep (b) of implanting the first semiconductor region with an impurityof a first conductivity type by a plasma doping method to thereby form afirst impurity region in an upper portion of the first semiconductorregion and a second impurity region in a side portion of the firstsemiconductor region, wherein in the step (b), a plasma doping method iscarried out under a first condition such that an implantation dose isequal to a first dose, and then a plasma doping method is carried outunder a second condition such that the implantation dose is equal to asecond dose smaller than the first dose.
 19. The method for producing asemiconductor device of claim 18, wherein: the step (b) is performed byusing a plasma generated from a gas containing the impurity; and aconcentration of the gas under the first condition is higher than thatof the gas under the second condition.
 20. The method for producing asemiconductor device of claim 18, wherein after the step (b), animplantation dose of the second impurity region is substantially equalto or greater than an implantation dose of the first impurity region.21. The method for producing a semiconductor device of claim 18, furthercomprising, before the step (a), a step of forming an insulating layeron the substrate, wherein the first semiconductor region is formed onthe insulating layer in the step (a).
 22. The method for producing asemiconductor device of claim 18, wherein the side surface of the firstsemiconductor region is a surface perpendicular to the upper surface ofthe first semiconductor region.
 23. The method for producing asemiconductor device of claim 18, wherein in the first impurity region,an implantation dose at a point in time when the plasma doping method iscarried out under the second condition is decreased from that at a pointin time when the plasma doping method is carried out under the firstcondition.
 24. The method for producing a semiconductor device of claim18, wherein: the step (b) is performed by using a plasma generated froma gas containing the impurity; and the gas containing the impuritycontains molecules B_(m)H_(n) (m and n are natural numbers) composed ofboron atoms and hydrogen atoms.
 25. The method for producing asemiconductor device of claim 18, wherein: the step (b) is performed byusing a plasma generated from a gas containing the impurity; and the gascontaining the impurity is a gas obtained by diluting moleculesincluding boron atoms with a rare gas.
 26. The method for producing asemiconductor device of claim 18, wherein: the step (b) is performed byusing a plasma generated from a gas containing the impurity; and a gascontaining the impurity is a gas obtained by diluting moleculesincluding the impurity with helium.
 27. The method for producing asemiconductor device of claim 18, wherein: the step (b) is performed byusing a plasma generated from a gas containing the impurity; and the gascontaining the impurity is a mixed gas of B₂H₆ and He.
 28. The methodfor producing a semiconductor device of claim 27, wherein aconcentration by mass of B₂H₆ in the mixed gas is greater than or equalto 0.01% and less than or equal to 1%.
 29. The method for producing asemiconductor device of claim 18, wherein: the step (b) is performed byusing a plasma generated from a gas containing the impurity; and the gascontaining the impurity contains BF₃, AsH₄ or PH₃.
 30. The method forproducing a semiconductor device of claim 18, further comprising, beforethe step (b), a step of implanting a semiconductor region which issimilar to the first semiconductor region and is provided in each of aplurality of dummy substrates with the impurity by a plasma dopingmethod under various conditions, so as to identify, as the firstcondition, a condition under which a sheet resistance of an impurityregion formed in a side portion of the semiconductor region takes anintended value, and so as to identify, as the second condition, acondition under which a sheet resistance of an impurity region formed inan upper portion of the semiconductor region takes an intended value.31. A method for producing a semiconductor device, comprising a step ofimplanting a semiconductor region with an impurity of a firstconductivity type by a plasma doping method to thereby form an impurityregion in the semiconductor region, wherein the step of forming theimpurity region comprises a step (a) of carrying out the plasma dopingmethod under a first condition such that an implantation dose is equalto a first dose, and after the step (a), a step (b) of carrying out theplasma doping method under a second condition such that the implantationdose is equal to a second dose smaller than the first dose.
 32. Asemiconductor device, comprising: a first semiconductor region formed ona substrate and having an upper surface and a side surface; a firstimpurity region of a first conductivity type formed in an upper portionof the first semiconductor region; and a second impurity region of afirst conductivity type formed in a side portion of the firstsemiconductor region, wherein a sheet resistance of the second impurityregion is substantially equal to or smaller than that of the firstimpurity region.
 33. A semiconductor device, comprising: a firstsemiconductor region formed on a substrate and having an upper surfaceand a side surface; a first impurity region of a first conductivity typeformed in an upper portion of the first semiconductor region; and asecond impurity region of a first conductivity type formed in a sideportion of the first semiconductor region, wherein a spreadingresistance of the second impurity region is substantially equal to orsmaller than that of the first impurity region.